Blood plasma is the liquid component of blood, in which the blood cells are suspended. Plasma is the largest single component of blood, making up about 55% of total blood volume. Blood plasma contains many vital proteins including fibrinogen, globulins and human serum albumin. Sometimes blood plasma can contain viral impurities which must be extracted through viral processing.

Serum refers to blood plasma in which clotting factors (such as fibrin) have been removed by the natural process of blood clotting.